Giveaway

If you are drawing a key, there's no problem. If you are drawing a game that you didn't buy before, and now it's removed... ask for the support to delete the giveaway.

ask for the winner to agree for delete or lose one slot for not deliver... or try to find out somewhere

A game that is removed from the Steam store can no longer be purchased on Steam. If you have a key for the game, you can still activate, download, and play the game anytime you want in the future. A Steam key should still work.